The present invention pertains to drills. More particularly, the present invention pertains to peck feed drills.
Peck feed drills are specially designed automatic drilling machines. Peck feed drills have particular application with exotic materials or when a smooth straight hole through a workpiece is absolutely essential. The greatest use of peck feed drills is in the aircraft industry.
The theory of operation of peck feed drills is easy to understand. A rotating drill bit moves into the workpiece being drilled, revolves a few turns, then retracts out of the workpiece. The retraction of the rotating drill bit from the workpiece causes the chip formed by the rotating drill bit to break off the workpiece and be extracted from the partially drilled hole. Because the rotating drill bit repeatedly returns to the workpiece until the hole is completely drilled, the process has become known as peck feed drilling.
To assure that the rotating drill bit is properly guided into the partially drilled hole in the workpiece, the rotating drill bit passes through a drill bushing. The drill bushing is held in place by a fixture. The fixture, in turn, is mounted to the workpiece. The drill bushing assures accurate positioning of the rotating drill bit each time it reenters the partially drilled hole.
Prior art peck feed drills have been either pneumatically or electrically operated. These prior art peck feed drills all have several things in common. First, they include a motor and gear assembly for rotating the drill bit. This is usually called a motor-gear quill. Second, they include a system for advancing and retracting the rotating drill bit. Third, they include a system for controlling the position and velocity of the rotating drill bit relative to the hole in the workpiece. This is usually called a feed control assembly.
Most critical in peck feed drilling systems is the feed control assembly. It is this system which governs the travel of the rotating drill bit. Control of the travel of the rotating drill bit just before it hits the bottom of the partially drilled hole and the actual advancement of the rotating drill bit while actually cutting metal at the bottom of the partially completed hole are essential.
Because of the complexity of peck feed drills and the mechanisms used to control them, most peck feed drills are found in large, fixed installations. This is because many of ordinary skill in the art believe that to assure a straight hole, the motor-gear quill and the system for advancing and retracting the rotating drill bit must be in a straight line. Such construction may be generally seen in U.S. Pat. No. 4,123,188.
The first significant departure from the straight line construction appeared in application Ser. No. 114,954 filed Oct. 30, 1987 now abandoned, to the same assignee. Therein, the motor-gear quill was placed off the centerline of the air cylinder which advanced and retracted the rotating drill bit. This re-location of the advancing and retracting mechanism off the center line of the rotating drill bit greatly reduced length and effectively made peck feed drills portable.
Portable peck feed drills have particular application when there is a large workpiece which cannot be moved to a fixed installation. One example of such a workpiece is an aircraft wing. It is more convenient to bring the peck feed drill to the wing rather than to bring the wing to the peck feed drill. This need to move peck feed drills easily and quickly to different workpieces has created an increasing need for smaller, more portable peck feed drills.
Size and weight are always key considerations when selecting portable peck feed drills. This is because the smaller the size and the lower the weight, the greater the utility of the peck feed drill. Therefore, a continuing need exists to develop a portable peck feed drill whose size and weight are small enough to enable the use of peck feed drilling techniques where they have never been used before. As with many power tools, small decreases in size are accompanied by great difficulties in design and manufacture. It must be recognized that while reducing the size and weight of peck feed drills is a design goal, there can be no compromise in the accuracy provided and the hole quality produced.